Microwave field rotator



Aprll 18, 1961 J. F. ZALESKI MICROWAVE FIELD ROTATOR Original. Filed Feb. 15, 1954 INVENTOR. JOHN F. ZALESKI BY W ATTORNEY 2,980,870 MICROWAVE FIELD RorAron John F. Zaleski, Valhalla, N.Y., assignor to General Precision, Inc., a corporation of Delaware 8 Claims. (-Cl. 333-7) This application is a division of my copending application Serial No. 410,154, filed February 15, 1954, and now abandoned, forfMicrowave Field Rotator.

It has recently been discovered that, when linearly polarized microwave energy is transmitted through certain ferrites subjected to a magnetic field, the plane of polarization of the microwave energy is rotated. This discovery, which is more fully discussed in United States Patent No. 2,644,930 to Luhrs and Tull, has led to the development of polarization rotators useful as elements in microwave transmission systems. A typical model employs a rod or tube of ferrite positioned along the axis of a short section of standard circular waveguide and held in place by a low-loss dielectric material which com- 7 pletely fills'the space between the rod and the waveguide walls. An axial magnetic field is applied to the rod by means of a permanent magnet or a solenoid on the outside surface of the waveguide. When microwave energy is propagated along the waveguide in the TE mode its plane of polarization is rotated, the direction and amount of rotation depending upon the polarity and intensity of the magnetic field applied to the ferrite rod but being independent of the direction of propagation of the micro wave energy. Rotations of more than ninety degrees in each direction have been obtained.

Although a polarization rotator such as above described has a number of useful applications, it is subject to certain inherent limitations. The magnetic field developed by the solenoid is inefiiciently coupled to theferrite rod because of the large external flux leakage paths and the V relatively great radial gap existing between the ferrite rodand the winding. Furthermore, if the solenoid be enerbe energized with direct current, but imposes severe limitations on the frequency and waveforms of an alternating current excitation.

It is an object of this invention to provide a ferromagnetic microwave polarization rotator. which may be excited with a high frequency alternating current.

Another object of the invention is to provide a polarization rotato-r having a lowinductance exciting winding.

Another object of the invention is to provide a polarization rotator in which the available magnetomotive force is utilized efliciently. 1

In accordance with the invention, the above stated objectives are attained by providing a low reluctance magnetic path between the source of magnetomotive force and the active polarization rotating element. The polarization rotating element comprises a hollow cylindrical ferrite tube which is imbedded in a dielectric material and positioned along the axis of a short section of cir- United States Patent 'ice cular Waveguide. The low reluctance path may be obtained by winding a solenoid about a soft iron core on the exterior of the waveguide and extending the core through the wall of the guide to the ferrite tube. The core extension is maintained at right angles to the lines of electric force of the microwave energy within the waveguide. The above construction provides a low reluctance path between the source of magnetomotive force and the ferrite tube resulting in efficient utilization of the available magnetomotive force.

For a clearer understanding of the invention reference may be made to the following detailed description and the accompanying drawing, in which:

Figure 1 is a sectional view of one embodiment of the invention; and

Figures 2 and 3 are isometric views of additional forms of the invention utilized as elements in power dividers.

Referring now to the drawing, there is shown in each figure a polarization-rotator comprising a short section of circular waveguide 11 completely filled by a low-loss dielectric material 12, except for a cylindrical space along the axis which is occupied by a hollow ferrite tube 13 and its associated elements. The dielectric material 12 is preferably a tetrafluoroethylene resin such as that sold under the trademark Teflon, and serves to support the ferrite tube 13. As is more fully explained in the aforementioned Patent No. 2,644,930, the tube 13 may consist of a number of different ferrites. For the sake of brevity, the term ferrite whenever used in this specification and the appended claims is intended to mean any of those ferrites which exhibit the polarization rotation properties herein referred to. One such ferrite which has been found satisfactory is known as Ferr'amic D and may be obtained from the General Ceramics and Steatite Corporation, Keasbey, New Jersey.

The circular waveguide 11 is provided with flanges 14 and 15' for connecting the polarization rotator to other microwave components. A rectangular input waveguide 16 having narrow sides 17 and 18 and a flange 19 is joined to the flange 14 of the circular guide 11. It has been found that a circular guide having an internal diameter of 0.75 inch and filled with a dielectric material such as previously described has a characteristic impedance very nearly equal to that of an air-filled rectangular guide with internal dimensions of 0.9 x 0.4 inch. It is therefore possible to join the circular guide 11 directly to the rectangular guide 16 with negligible power loss. The input guide'16 is assumed to be propagating microwave energy in the dominant T'E mode so that the lines of electric force are parallel to the narrow sides 17 and 18. This wave energy will, of course, enter the circular guide 11 in the dominant TE- mode.

Referring now to Fig. 1, there is shown within the ferrite tube 13 a ferromagnetic core 47 which extends axially for a short distance into the input waveguide 16. The core 47 is then bent and, being kept parallel to the broad sides of the input guide 16, is led to the exterior of guide 16 through an aperture in the narrow side 17.

The bend in the core may conveniently comprise two forty-five degree bends as shown, but other arrangements could be used, it only being necessary to keep the axis of the core in the median plane parallel to the broad sides of guide 16. At the end where the core 4 7 emerges from the guide '16, it has a solenoid 48 wound around it to provide the magnetic field necessary 3 any other angle may be used to suit the particular application.

-In operation, the lines of magnetic force generated by the solenoid 48:- emerge. from the end 49 of the core. In returning to. the opposite? end ofthe core, the lines of magnetic force will pass through the ferrite tube 13 thus providing a longitudinal magnetic field through the tube 13. It is obvious that the proximity of the, core. 47- and especially its end 49 to the tube 13 provides a magnetic path having a much lower reluctance than if the solenoid. were wound on. the outside of the circular guide. '11..

Fig. 2 shows the use of a polarization rotator somewhat similar to. that of Fig. 1. to form. a microwave power divider. A. section of circular waveguide 54 is joined by means of a: flange 55 to the flange. 15 of. wave,- guide. 1.1,. A of rectangular waveguides 56. and 57 are secured to the periphery of the guide 54 with their broad. sides parallel to the axis of. guide 54; so as to form twov mutually perpendicular H-plane junctions. with the; circular guide 5-4. The end of circular guide 54 is closed by means of a conductive plate '58 which is positioned an integral number of half guidewavelengths from. the near narrow sides of the rectangular guides 56 and 57.v

Within the ferrite tube 13 is a cylindrical ferromagnetic core 59 which extends axially through the guide 54' The operation of thefpolarization rotator is similar to that described in connection with Fig. 1. The end of the core 59 acts as a source of magnetic flux lines and these lines in returning .to the solenoid provided a of magnetic flux through the tube 13 where it is needed.

Although the invention has been described with respect to several specific embodiments many modifications may be made within the scope of the invention.

Although a tubular shape is at present preferred for the ferrite member, other shapes, such as a solid rod or bar, could be used. Many other modifications will occur to those skilled in the art.

What is claimed is:

1. A microwave polarizationv rotator comprising, a circular waveguide, said waveguide comprising a hollow cylindrical ;-conductive pipe open at both ends and capable oftransmitting microwave energy therethrough in the axial direction, a ferrite tube. within said waveguide and coaxial therewithfa solenoid located outside said waveguide, and a ferromagnetic rod projecting into the interior of said solenoid and extending into but substantiall'y magnetically insulated from said tube for substantially the'entire length thereof. I

2. A microwave polarization rotator comprising, a circular waveguide," said waveguide comprising a hollow cylindrical conductive pipe open at both ends, a hollow" cylindrical ferrite tube positioned coaxially within said waveguide, a solenoid outside of said waveguide, and a ferromagnetic rod projecting into the interior of said solenoid and extending into but substantially magnetically insulated from said ferrite tube for substantially the cular waveguide, said waveguide comprising a hollow longitudinal magnetic field through the ferrite tube 13.

The operation of the power divider is believed to be obvious from the drawing. If no current flows through the winding 61, energy from the input guide 16 will pass through -the rotator with no change in polarization and will be coupled to the rectangular guide 56. cient current flows through winding 61, the plane of polarization can be rotated through ninety degrees and all of the, input power will appear in guide 57. At intermediate values of current through solenoid 61, the power will divide between guides 56 and 57.

Referring now to .Fig. 3, there is shown a device similar to that shown in Fig. 2. The circular guide 11, the input guide 16, the circular waveguide 54 with its associated rectangular guides 56 and 5'1 are the same as in'Fig, Abutting the ferrite. tube 13 is a. tubular ferromagnetic core 63 having approximately the. same diameter and thickness as the tube 13. The core 63- 64. to the exterior of the system. A pair of U-shaped i ferromagnetic members 67 and 68 have one leg of each joined to theend of tubular core 63 while their other legs are joined to the cylindrical core 6 5. A solenoid 69 is wound around the core 65 between the legs of the U-shaped members 67- and 68.

The operation of the embodiment of Fig. 3 is similar to that of the embodiment. of Fig. 2. The advantage of the construction shown in Fig. 3 is the completely closed ferromagnetic path of very low reluctance which extends from each end. of. the tube 13 to the solenoid. By this construction, there is a maximum concentration cylindrical conductive pipe open at both ends and capable of transmitting microwave energy therethrough in the axial direction, a hollow cylindrical ferrite tube within said circular waveguide and coaxial therewith, a

'- rectangular waveguide joined coaxially to saidcircular containing a bend, one erid of said rod projecting through a narrow side of said-rectangular waveguide to the exterior thereof and the. other end extending into but substantially magnetically insulated from said tube for substantially the entire length thereof, and a solenoid on said one end of said rod.

- 4. A microwave power divider comprising, a first circular'waveguide', said first circular waveguide comprisinga' hollow cylindrical conductive pipe open at bothends and capable of transmitting; microwave energy there through in the axial direction, a'hollow cylindrical fer r-ite .tubewithin said waveguide coaxial therewith, a second circular'waveguide having: one end joined coaxially toisaid first; circular waveguide, a plurality of W rectangular waveguides coupled to and spaced around the periphery-of, saidsecond waveguide, a conductive plate closing the other end of said second circular waveguide, a ferromagnetic rod along the axi's'of said circular'wave'guides, one end of said rod projecting into but substantially magnetically insulated from said tube end of said rod protruding through an aperture in said plate, and a solenoid around said other end of said rod.

"5 .'A microwave power divider comprising, a first circular waveguide, said first circular waveguide comprising a hollow cylindrical conductive pipe open at both ends and capable of transmitting microwave energy therethrough in the axial direction, a hollow cylindrical ferrite tube within said waveguide and coaxial therewith, a second circular waveguide. having one end joined co-- axially to said first circular waveguide, a plurality of rectangular waveguides coupled to and, spaced around the periphery of said second waveguide, a conductive plate closing the other end of said second waveguide, a hollow cylindrical ferromagnetic tube along the axis of said waveguides one end of which abuts said ferrite tube and the other end of which projects through an aperture in said plate, a ferromagnetic rod positioned coaxially within both said ferrite tube and said ferromagnetic tube, said rod extending into but substantially magnetically insulated from said ferrite tube for substantially the entire length thereof, said rod also protruding beyond said other end of said ferromagnetic tube, a solenoid wound around the protruding portion of said rod, and a ferromagnetic path connecting said rod and said ferromagnetic tube.

6. A microwave polarization rotator comprising, a hollow conductive pipe wave transmission means includ ing a section of waveguide having a circular cross section and being open at both ends, said section of waveguide being capable of transmitting microwave energy therethrough in the axial direction, a hollow cylindrical ferrite tube positioned coaxially within said section of waveguide, a ferromagnetic rod having its first end extendingwithinand substantially magnetically insulated from said tube for substantially the entire length thereof and its second end extending to the exterior of said wave transmission means, said rod being so positioned relative to the walls of said transmission means that the lines of electric force of any wave energy being transmitted through said wave transmission means in the dominant mode are perpendicular to the axis of said rod, and a solenoid wound on said second end of said rod.

7. A microwave polarization rotator comprising, a first circular Waveguide, said first circular waveguide comprising a hollow cylindrical conductive pipe open at both ends and capable of transmitting microwave energy therethrough in the axial direction, a hollow cylindrical ferrite tube within said waveguide coaxial therewith, a second circular waveguide having one end joined coaxially to said first circular waveguide, a conductive plate closing the other end of said second circular waveguide, a ferromagnetic rod along the axis of said circular waveguides, one end of said rod extending within but substantially magnetically insulated from said tube for substantially the entire length thereof and the other end of said rod protruding through an aperture in said plate, and a solenoid around said other end of said rod.

8. A microwave polarization rotator comprising, a first circular waveguide, said first circular waveguide comprising a hollow cylindrical conductive pipe open at both ends and capable of transmitting microwave energy therethrough in the axial direction, a hollow cylindrical ferrite tube within said waveguide and coaxial therewith, a second circular waveguide having one end joined coaxially to said first circular waveguide, a conductive plate closing the other end of said second waveguide, a hollow cylindrical ferromagnetic tube along the axis of said waveguides one end of which abuts said ferrite tube and the other end of which projects through an aperture in said plate, a ferromagnetic rod within both said ferrite tube and said ferromagnetic tube, said rod extending into and substantially magnetically insulated from said ferrite tube for substantially the entire length thereof, said rod also protruding beyond said other end of said ferromagnetic tube, a solenoid Wound around the protruding end of said rod, and a ferromagnetic path connecting said rod and said ferromagnetic tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,197,123 King Apr. 16, 1940 2,630,492 Muchmore Mar. 3, 1953 2,645,758 Van de Lindt July 14, 1953 2,650,350 Heath Aug. 25, 1953 2,671,884 Zaleski Mar. 9, 1954 2,719,274 Luhrs Sept. 27, 1955 2,776,412 Sparling Jan. 1, 1957 2,825,765 Marie Mar. 4, 1958 2,832,054 Fox Apr. 22, 1958 2,844,789 Allen July 22, 1958 2,847,647 Zaleski Aug. 12, 1958 2,849,684 Miller Aug. 26, 1958 2,850,705 Chait et a1. Sept. 2, 1958 FOREIGN PATENTS 980,648 France Dec. 27, 1950 667,290 Great Britain Feb. 27, 1952 OTHER REFERENCES Fox et a1: Bell System Technical Journal, vol. 34, No. 1, January 1955, pages 5-103 (pages 37-42 relied on).

Caswell: Electronics, October 1953, page 252. 

